This is a randomized, double-blind, placebo controlled, multicenter parallel group comparison study designed to evaluate the efficacy of chronic, passive antibody immunotherapy employing one of two dosed of a mucoid exopolysaccharide Pseudomonas Aeruginosa immune globulin, intravenous (human) (MEP IGIV) in cystic fibrosis (CF) patients with endobronchial colonization by mucoid Pseudomonas aeruginosa.